Trumpy,

Let's hear it for google image search [Linked Image] In the below link you will see a good picture of a trail running under the sort of lines that one sees in North America.
http://www.alternativerunning.com/trailnotes/cubrun.htm

Usually there are no barriers other than height and the towers themselves. When the towers are in urban areas, sometimes the tower base is fenced in.

Usually the conductors cross roads at a pretty high elevation, but I've been in parking lots positioned below center cable span where the conductors are pretty low. I've found it very disquieting to be under a multi-kV line in a light snow, hearing both a bit of 60 Hz hum and the crackle of snow flakes interacting with the line and the insulators.

-Jon